I was in MTY a month or so ago. Nice airport, passport control get you through fairly quickly, just have your forms filled out correctly. As for a Skyteam lounge, the Aeromexico lounge is very nice and is located
here in the airport. It is located on the same level as the passport control (you can see it directly behind you when you are standing in the line behind the security glass) and next to the small AMEX lounge.
Many good places to eat. ^